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What is the space complexity of the top-down memoization solution for Equal Partition with n elements and total sum S?

medium🪤 Complexity Trap Q6 of Q15
Dynamic Programming: Knapsack - Equal Partition (Partition Equal Subset Sum)
What is the space complexity of the top-down memoization solution for Equal Partition with n elements and total sum S?
AO(n * S)
BO(S)
CO(n + S)
DO(n)
Step-by-Step Solution
Solution:
  1. Step 1: Analyze memoization storage

    Memo stores results for states (i, curr_sum), total O(n * S) entries.
  2. Step 2: Consider recursion stack

    Recursion stack depth is O(n), memo size O(n*S), but stack is separate.
  3. Final Answer:

    Option A -> Option A
  4. Quick Check:

    Space = memo + recursion stack = O(n*S) + O(n) ≈ O(n*S) [OK]
Quick Trick: Memo + recursion stack space combined [OK]
Common Mistakes:
MISTAKES
  • Ignoring recursion stack space
  • Assuming only memo space counts
Trap Explanation:
PITFALL
  • Candidates often forget recursion stack adds to space complexity.
Interviewer Note:
CONTEXT
  • Tests understanding of auxiliary space in recursive DP
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